4

AT88RF020

2010C–RFID–2/06

Anticollision

Anticollision is implemented as per ISO 14443-3, Type B (see ISO 14443-3, sections 7.3

and 7.4). There are four primitive commands that support the anticollision scheme:

REQB/WUPB, SlotMARKER, ATTRIB and HLTB.

REQB/WUPB Command

This 5-byte command (see ISO 14443-3, section 7.7) is used for the PCD to probe the

field for PICCs or to wake up PICCs that are in the HALT state. The first byte must be a

fixed 0x05. This chip will respond only to values of 0x00 or 0x01 in the second (AFI)

byte. Bit 3 of the third byte is used to select between REQB and WUPB commands,

while Bits 0–2 are used to set N, which is used for the command response (ATQB). If

the PICC receives a WUPB command with an invalid AFI code, then it will remain in the

HALT state.

When the PICC receives one of these commands properly encoded, it will generate a

random number (R) of up to four bits, according to the value of N passed by the PCD

and specified in Table 13 of ISO 14443-3 and in Table 2 on page 4. If N = 1 or the ran-

dom number generator selects R = 1, then the PICC will send an ATQB and listen for

REQB/WUPB, ATTRIB and HLTB commands. Otherwise, it will wait for the Slot-

MARKER command that matches the value R selected by the random number

generator.

The response to both of these commands is an ATQB packet. This format is as speci-

fied in ISO 14443-3, section 7.9.1, with the following values:

ATTRIB Command

The ATTRIB command is used to select among all the chips that may have responded

to a given REQB/WUPB command. The chip will respond to ATTRIB commands from

11 to 16 bytes in length where the 2nd, 3rd, 4th and 5th bytes exactly match the PUPI

stored in the memory. If the chip responds to the ATTRIB command, it enters the

ACTIVE state where the data transfer commands described above will be honored.

Table 2. Command Codes

Binary Code (in cmd)

N

Size of R (in bits)

000

1

–

100

2

1

010

4

2

110

8

3

001

16

4

PUPI:

As stored in memory (unique serial number)

Application Data:

As stored in memory

Protocol Info:

0x00, 0x00, 0x41

(Bit_rate_capability: 106 Kbps only)

(Max_frame_size: 16)

(Protocol type: not compliant with 14443-4)

(FWI: Frame Waiting Time minimal, 4.8 ms)

(ADC: Application Data Coding is proprietary)

(FO: Only CID (Card Identifier) supported by PICC)